Today, fats and fatty acids primarily come from vegetable and animal sources, with the notable exception of commercial production of omega-3 fatty acids by fermentation of microbes for use in baby formula and nutritional supplements. Progress is being made however toward the commercial production of tailored oils using recombinant microalgae. See PCT Publications WO2008/151149, WO2010/06032, WO2011/150410, WO2011/150411, and international patent application PCT/US12/23696.
One method for producing a desired fatty acid profile in an oleaginous organism is to introduce an acyl-ACP thioesterase transgene; e.g., a transgene from a plant that produces a desired fatty acid.
By terminating fatty acid biosynthesis, the acyl-acyl carrier protein (ACP) thioesterase (TE) functionally determines the length and identity of the fatty acid end product (Salas et al., (2002) Archives of Biochemistry and Biophysics 403: 25-34). Based on amino acid sequence alignments, the plant TEs have been shown to cluster into two families, FatAs, which show marked preference for 18:1-ACP with minor activity towards 18:0- and 16:0-ACPs; and FatBs, which hydrolyze primarily saturated acyl-ACPs with chain lengths that vary between 8-16 carbons (Voelker, In Genetic Engineering Volume 18. Edited by: Setlow J K. New York, Plenum Press; 1996:111-133; Ginalski, et al., Nucl Acids Res (2003) 31:3291-3292; and Jones, et al., (1995) Plant Cell 7: 359-371). FatB TEs have a conserved hydrophobic 18-amino acid domain (Facciotti and Yuan (1998) European Journal of Lipid Science and Technology 100:167-172), and a conserved Asn-His-Cys catalytic triad in the C-terminal catalytic domain (Blatti, et al., PLoS ONE (2012) 7(9): e42949. doi:10.1371 and Mayer and Shanklin, BMC Plant Biology (2007) 7:1-11). Mayer and Shanklin, BMC Plant Biology (2007) 7:1-11, identify a C-terminal conserved acyl-ACP thioesterase catalytic domain characterized by a C-terminal hot dog fold encompassing the Cys-His-Asn catalytic triad. The conserved acyl-ACP TE catalytic domain is well-characterized and has been assigned conserved domain accession number pfam01643. The hot dog fold is also well-characterized and has been assigned conserved domain accession number cd03440 and is part of the hotdog superfamily assigned conserved domain accession number c100509.